I just bought a 2011 Duramax and I'm trying to figure out if the def has been removed or not. The tank is there but it smokes like an old school motor.

 

1-on a diesel white smoke can be from overfueling...when diesel burns at low combustion temps...check the injector balance rates

2-check if the coolant reservoir is pressurized....indicating headgasket issues

3-if you want to disable the def injector for testing purposes...unplug the def injector.